Stabilization of Medium-Frequency Modes in Isolated Microgrids Supplying Direct Online Induction Motor Loads

Driven by the economical and environmental concerns, the importance of distributed generation-based microgrids is increasing. However, the presence of induction motor (IM) loads in converter-based microgrids might induce source-load admittance mismatch between the IM load and microgrid converters leading to medium-frequency instabilities, particularly in isolated microgrids. To overcome this issue, this paper presents detailed small-signal admittance models, analysis, and stabilization of a voltage-source inverter (VSI)-based microgrid with direct online IM load. The resultant source (VSI) and load (IM) admittances form a multi-input-multi-output (MIMO) system. Using the generalized Nyquist stability criterion, it is shown that the interactions between the lightly-damped dynamics of IMs and isolated VSI-based microgrid have significant destabilizing effect. Active compensation techniques are proposed to maintain the system stability. Time-domain simulations and experimental results are presented to validate the theoretical analysis.